CN108988397B - Parallel operation power distribution control method for energy storage converters - Google Patents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
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Abstract
The invention relates to a parallel operation power distribution control method of energy storage converters, which is characterized in that on the premise of meeting the normal operation of a parallel system, power disturbance is carried out on each converter unit, the THD of a grid-connected point is detected in real time in the power disturbance process, the disturbance is stopped when the THD is minimum, the power when the THD is minimum is set as the output power set value of the corresponding converter unit, and then the output power set value corresponding to each converter unit is obtained, so that the power distribution is realized. The power distribution method aims at minimizing the THD of the grid-connected point, can accurately obtain the output power of each converter unit, takes the output external characteristic of the parallel operation of the converters as a control basis, and provides technical support for the parallel development of the energy storage converters. In addition, the output power of each converter unit obtained by the distribution method controls each converter unit, so that the THD of the system can be minimized, the requirement of stable operation of the system can be met, and the external characteristics of the AC side of the system can be improved.
Description
Technical Field
The invention relates to a parallel operation power distribution control method for energy storage converters, and belongs to the technical field of parallel operation of the energy storage converters.
Background
With the rapid development of new energy technologies such as photovoltaic, wind power and the like, the capacity of new energy such as photovoltaic, wind power and the like is increased more and more, but the new energy such as photovoltaic, wind power and the like has great randomness and is difficult to meet the demand of scheduling, so that the grid connection difficulty of the new energy such as photovoltaic, wind power and the like is great, and further development of the new energy such as photovoltaic, wind power and the like is limited. One of the methods for solving the problem is to introduce an energy storage system to stabilize the output of a photovoltaic power generation system, a wind power generation system and other new energy power generation systems. With the increasing of the capacity of photovoltaic and wind power, the requirement on the grid-connected capacity of an energy storage system is higher and higher, but the increase of the capacity of power electronic equipment often brings about a sharp rise in cost, and the expansibility of the system is poor due to the adoption of the mode. In order to solve the above problems, a parallel converter system is a good solution. As shown in fig. 1, a typical distributed system includes a wind power generation device and a converter thereof, a photovoltaic power generation device and a converter thereof, and an energy storage device and an energy storage converter parallel system thereof, where the energy storage converter parallel system uses a common dc bus and a common ac bus, and certainly, may also use a common ac bus. The energy storage converter parallel system is formed by connecting n converter modules in parallel, the number of n is set according to actual needs, and the converter modules are DC/AC modules. However, in the energy storage converter parallel system, parameter differences exist among the converters, and power distribution is difficult to guarantee, so that the external characteristics of the converter parallel system are affected, the difficulty of the converter parallel system being incorporated into a power grid is increased, even the converter parallel system is difficult to be connected to the power grid, even if the converter parallel system is incorporated into the power grid, the Total Harmonic Distortion (THD) of a grid-connected point is large, and the requirement of stable operation of the system is not met.
The output distribution of the current converters in parallel operation only considers the parallel operation of the converters with the same rated power, and the adjustment target mainly aims at that the output power of each converter in parallel connection does not exceed the rated power of the converter, and the output power of each converter is equal. There is no method for controlling the output external characteristics of the parallel operation of the converters. Therefore, a parallel control method based on the output external characteristics of the parallel operation of the converters is urgently needed, otherwise, the output external characteristics of the parallel operation of the converters becomes a bottleneck for further improving the grid-connected capacity of the converters.
Disclosure of Invention
The invention aims to provide a parallel operation power distribution control method for energy storage converters, which is used for solving the problem that the power distribution method in the traditional parallel operation mode of the converters can cause a grid-connected point THD to be larger.
In order to achieve the purpose, the scheme of the invention comprises a power distribution control method for parallel operation of energy storage converters, which is characterized in that on the premise of meeting the normal operation of a system, power disturbance is carried out on each converter unit, in the process of power disturbance, the THD of a grid-connected point is detected in real time, when the THD is minimum, the disturbance is stopped, the power when the THD is minimum is set as the output power set value of the corresponding converter unit, and then the output power set value corresponding to each converter unit is obtained, so that the power distribution is realized; the converter unit is a converter module or is composed of at least two converter modules.
The conditions for normal operation of the system include: the output power of each converter module does not exceed the rated power of the module, the total output power of the parallel system does not exceed the rated power of the system, and the THD of the grid-connected point does not exceed the standard.
Before power disturbance is carried out on each converter unit, the output power of each converter module is adjusted, so that the total output power of a parallel system does not exceed the rated power of the system, and the output power of each converter module does not exceed the rated power of the module.
For any converter unit, in the process of power disturbance, if the corresponding grid-connected points THD are equal and minimum when at least two times of disturbance are carried out, comparing the THD of the output side of each converter unit corresponding to each disturbance, finding the power disturbance with the minimum THD fluctuation of the output side of the converter unit, and taking the power of the converter unit corresponding to the power disturbance as the output power set value of the converter unit.
On the premise of meeting normal operation, performing power disturbance on any one converter unit, detecting the THD of a grid-connected point in real time in the power disturbance process, stopping disturbance when the THD is minimum, setting the output power of the grid-connected point when the THD is minimum as the output power of the converter unit, and performing operation on the converter units which are not adjusted according to the steps to obtain the output power of other converter units so as to obtain a group of distribution combinations of the output power, wherein if the distribution combinations are used for controlling the converter units, the THD of the grid-connected point of a parallel system can be minimum. The power distribution method aims at minimizing the THD of the grid-connected point, can accurately obtain the output power of each converter unit, takes the output external characteristic of the parallel operation of the converters as a control basis, and provides technical support for the parallel development of the energy storage converters. In addition, when the output power of each converter unit obtained by the distribution method is used for controlling each converter unit, the THD of the system can be minimized, the requirement of stable operation of the system can be met, and the external characteristics of the AC side of the system can be improved.
In addition, the method is suitable for dynamic output distribution control of a parallel system formed by energy storage converters with the same or different rated powers connected in parallel.
Drawings
FIG. 1 is a topological structure diagram of a distributed system including a parallel system of energy storage converters;
FIG. 2 is a schematic flow chart of a power distribution control method for parallel operation of energy storage converters;
FIG. 3 is a topological block diagram of one embodiment of a parallel system of energy storage converters;
fig. 4 is a schematic diagram of a grid-connected point THD without using the power distribution control method provided by the present invention;
FIG. 5 is a schematic diagram of a grid-connected point THD optimized by the power distribution control method provided by the present invention;
fig. 6 is a topological structure diagram of another embodiment of the parallel system of the energy storage converters.
Detailed Description
Embodiment of power distribution control method for parallel operation of energy storage converters
The invention provides a parallel operation power distribution control method of energy storage converters, which is characterized in that on the premise of meeting the normal operation of a parallel system, power disturbance is carried out on each converter unit, THD of a grid-connected point of an alternating current bus is detected in real time in the power disturbance process, the disturbance is stopped when the THD is minimum, the power when the THD is minimum is set as an output power set value of the corresponding converter unit, and then the output power set value corresponding to each converter unit is obtained, so that the power distribution is realized; the converter unit is a converter module or is composed of at least two converter modules.
The parallel operation power distribution control method of the energy storage converters is further described in detail with reference to the attached drawings.
When power distribution is carried out, the parallel system is required to be in a normal operation state, and the normal operation conditions comprise: the output power of each converter module does not exceed the rated power of the module, the total output power of the parallel system does not exceed the rated output power of the system, and the THD of the grid-connected point does not exceed the standard, namely does not exceed the national standard. Of course, if the parallel system is not in a normal operation state, the system needs to be adjusted first, and then subsequent output distribution, i.e., power distribution, is performed. The adjusting process specifically comprises the following steps: and adjusting the output power of each converter module to ensure that the total output power of the parallel system does not exceed the rated power of the system and the output power of each converter module does not exceed the rated power of the module.
For any one converter unit in the parallel system, the converter unit is a set concept, can refer to one converter module, and can also be formed by at least two converter modules. If the converter unit refers to a single converter module, the power obtained by the power distribution method acts on the converter module, and if the converter unit refers to at least two converter modules, the power obtained by the power distribution method needs to act on all the converter modules referred to by the converter unit, and all the converter modules are controlled to output the obtained power in total. In the embodiment, the converter unit refers to a converter module as an example, that is, the converter unit is the converter module.
Then, for any one converter module in the parallel system, the power disturbance is performed on the converter module to increase the power or decrease the power. And in the power disturbance process, detecting the THD of the grid-connected point in real time, judging the THD of the grid-connected point, continuing to disturb when the THD is gradually reduced until the THD of the grid-connected point is minimum, stopping disturbing when the THD is minimum, and setting the power of the converter module at the moment when the THD is minimum as the set value of the output power of the converter module. If the power is increased as an example, the power is increased for the converter module, the THD of the grid-connected point is detected in real time, when the THD is gradually reduced, the power is continuously increased until the THD of the grid-connected point is minimum, when the THD is minimum, the power is stopped to be increased, and the power of the converter module at the moment, namely when the THD is minimum, is set as the output power set value of the converter module.
The obtained output power of one converter module is an output power set value and is recorded, the converter module is controlled according to the obtained output power set value at the moment, then one of the remaining modules is controlled according to the process, the obtained output power of the converter module is an output power set value and is recorded, the converter module is controlled according to the obtained output power set value at the moment, then another converter module in the remaining modules is controlled according to the process, and the rest is repeated, so that the output power set values of all the converter modules can be obtained. Therefore, through the process, each converter module has an output power set value, and power distribution of the converter modules of the parallel system is realized. Furthermore, as can be seen from the above process, a certain converter module (for convenience of description, referred to as a first converter module) is controlled to obtain an output power set value, and the converter module is controlled to operate according to the set value; then, the second converter module is controlled to obtain an output power set value, the second converter module can be controlled to operate according to the set value, and then the first converter module and the second converter module operate according to the corresponding output power set value; then, the third converter module is controlled to obtain an output power set value, the third converter module can be controlled to operate according to the set value, and then the first converter module, the second converter module and the third converter module operate according to the corresponding output power set values; and analogizing in sequence, the more the converter modules are operated at the corresponding output power set value. For the last converter module, since the total output power of the system is determined, the output power of other converter modules is also determined, and the output power of the last module can be directly obtained. All converter modules operate according to the corresponding output power set values, and the THD of the grid-connected point is minimum.
And the power disturbance to the converter module is carried out according to times, and the interval time between two adjacent times and the disturbance period are set according to the actual situation. For a certain converter module, in the power disturbance process, if the THDs corresponding to at least two times of disturbance are equal and are all minimum values, that is, it is assumed that the THD of a grid-connected point corresponding to the mth disturbance is smaller than the THD corresponding to the M-1 th disturbance, the THD of a grid-connected point corresponding to the M +1 th disturbance is equal to the THD corresponding to the mth disturbance, the THD of a grid-connected point corresponding to the M +2 th disturbance is equal to the THD corresponding to the M +1 th disturbance, … …, the THD of a grid-connected point corresponding to the M + S th disturbance is equal to the THD corresponding to the M + S-1 th disturbance, and the THD of a grid-connected point corresponding to the M + S +1 th disturbance is greater than the THD corresponding to the M + S-1 th disturbance (S + S is greater than or equal to 1), that is, that S +1 THD minimum values are provided. Then, detecting the THD of the output side of each converter module in the parallel system corresponding to each disturbance from the mth disturbance to the mth + S disturbance, comparing the THD of the output side of each converter module in the parallel system corresponding to each disturbance in the mth disturbance to the mth + S disturbance, and finding the power disturbance with the minimum THD fluctuation at the output side of the converter module, where the determination method may be: and judging the error value of the THD at the output side of the largest converter module and the error value of the THD at the output side of the smallest converter module in each disturbance, and finding the smallest error value to correspond to the smallest THD fluctuation. For example, the THD fluctuation at the output side of the converter module corresponding to the M + S th disturbance is the minimum, and then the power of the converter module corresponding to the disturbance, that is, the output power of the converter module corresponding to the M + S th disturbance is used as the set value of the output power of the converter module.
Certainly, in order to detect the grid-connected point THD of the ac bus and the THD of the output side of each converter module, a special detection device, such as a harmonic current analyzer, needs to be arranged at the grid-connected point and the output side of each converter module.
Fig. 2 shows an embodiment of the power distribution control method for parallel operation of the energy storage converters, but the invention is not limited to the embodiment shown in fig. 2.
Fig. 3 is a parallel system formed by three converter modules connected in parallel, and the power distribution method is illustrated below by taking fig. 3 as a specific application example.
When the three converter modules are connected in parallel, the output power distribution condition of each module needs to be considered according to the output power of the whole parallel system. If the parallel system is close to an ideal operation state, for example, when the output power of the parallel system is close to the rated power, the three converter modules can work under the state close to the rated power, and at the moment, the system does not need to adjust the output power.
However, in general, the operation state of the system is not ideal, for example, when the output power of the parallel system is low, the output distribution control consideration of each module is required. When the actual output power of the module is smaller than the rated output power, the distribution problem of the output power of each module needs to be considered. The parallel system of the energy storage converters is a grid-connected system, actual grid-connected requirements need to be met, and meanwhile, considering feasibility of the whole control method, the specific operation steps of the power distribution method are as follows:
obtaining and recording a grid-connected point THD value before adjustment as an initial value for comparison;
the converter module 1 is selected as a control object, power disturbance is carried out on the parallel system on the premise of ensuring stable operation of the parallel system, for example, increase is taken as an example, the THD condition of the grid-connected point is monitored, if the THD is gradually reduced, the power output of the module is continuously increased, and certainly, if the THD is increased, the power output of the module can be reduced. When the THD is changed from reduction to increase, namely when the THD is minimum, the output power of the module at the moment is recorded as the set value of the output power of the module, the operation of the module is controlled by the set value, and then the module 2 is controlled according to the process. For module 3, since the total output power of the system is determined, after obtaining the output power of module 1 and module 2, the output power of module 3 can be obtained by subtracting the output power of module 1 and the output power of module 2 from the total output power of the system.
In the adjusting process, the situation that the power of each module is different, but the THD at the grid-connected point of the parallel system is the same may be encountered, that is, in the power disturbance process, the situation that the THD corresponding to at least two disturbances is equal and is the minimum value may occur, and at this time, the power distribution combination which enables the THD of each module to be closest, that is, the fluctuation is the minimum, is preferentially considered.
In addition, since the total output power of the system is known, when n converter modules are connected in parallel in the system, only n-1 converter modules need to be controlled, and the last converter module can be calculated according to the total output power and the set values of the output modules of other modules.
Fig. 4 is a schematic diagram of a grid-connected point THD without using the power allocation control method provided by the present invention, and fig. 5 is a schematic diagram of a grid-connected point THD optimized by using the power allocation control method provided by the present invention.
The specific embodiments are given above, but the present invention is not limited to the described embodiments. The basic idea of the invention lies in the basic process of the power distribution control method for parallel operation of energy storage converters, and the control method is not limited to the parallel system shown in fig. 1, but also can be applied to the parallel system shown in fig. 6, in short, the method is applied to the parallel energy storage system of the common alternating current bus. Variations, modifications, substitutions and alterations may be made to the above-described embodiments without departing from the principles and spirit of the invention, and still fall within the scope of the invention.
Claims (4)
1. A parallel operation power distribution control method for energy storage converters is characterized in that power disturbance is sequentially carried out on converter units on the premise that normal operation of a system is met, THD of grid-connected points is detected in real time in the power disturbance process, disturbance is stopped when THD is minimum, the power when THD is minimum is set as an output power set value of the corresponding converter unit, and then output power set values corresponding to the converter units are obtained, so that power distribution is realized;
the converter unit is a converter module or is composed of at least two converter modules.
2. The parallel operation power distribution control method for the energy storage converters as claimed in claim 1, wherein the normal operation conditions of the system include: the output power of each converter module does not exceed the rated power of the module, the total output power of the parallel system does not exceed the rated power of the system, and the THD of the grid-connected point does not exceed the standard.
3. The method for controlling the power distribution of the parallel operation of the energy storage converters as claimed in claim 1 or 2, wherein before the power disturbance is performed on each converter unit, the output power of each converter module is adjusted, so that the total output power of the parallel system does not exceed the rated power of the system, and the output power of each converter module does not exceed the rated power of the module.
4. The method for controlling the power distribution of the parallel operation of the energy storage converters as claimed in claim 1, wherein in the power disturbance process of any one converter unit, if the corresponding grid-connected points THD are equal and minimum when at least two disturbances are performed, comparing the THD of the output side of each converter unit corresponding to each disturbance, finding the power disturbance with the minimum THD fluctuation of the output side of the converter unit, and taking the power of the converter unit corresponding to the power disturbance as the set value of the output power of the converter unit.
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